"Your top server error codes" email from Cloudflare

Every week we receive an automated email from Cloudflare titled, “Your top server error codes”

It lists a bunch of domains with “origin errors as a % of total requests” and says we have upward of 22% 503 errors for each domain.

It goes on to say, “These errors indicate issues with your origin web servers, possibly caused by server overload, crashes or network failures”

I am pretty sure there is nothing wrong with our origin server, and it isn’t returning 5xx errors. However, we do have “JS Challenge” turned on within Cloudflare for all visitors outside of our country. I believe that Cloudflare returns a “503 service temporarily unavailable” error when a bot or such like fails the JS challenge.

So am I safe in assuming that these 503 errors are actually just failed JS challenges, and not actually something wrong with our origin? I wanted to check, because the wording in the email from Cloudflare kind of implies otherwise.


As you are writing due to JS challenge it could be the one statement:

  • We do count 503 errors from your origin that are passed as a response from the edge, though in this version 503 errors from the edge have multiple potential sources.:

    • Cloudflare detected malicious Layer 7 traffic and automatically issued a JS challenge that blocked the request

From the link here:

It does not necessarily failed JS challenges - every JS challenge issued to the visitor will return 503, if the visitors’ browser can solve the JS challenge then the webpage will be returned with HTTP 200.

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